1. Field of the Invention
The present invention relates to a liquid crystal display device and a method for driving a liquid crystal display, and more particularly to a liquid crystal display device which applies AC pulses to a liquid crystal layer through a plurality of scan electrodes and a plurality of data electrodes which face and cross each other and a method for driving a liquid crystal display.
2. Description of Related Art
In recent years, various kinds of reflective type liquid crystal displays which use liquid crystal which exhibits a cholesteric phase at room temperature (mainly, chiral nematic liquid crystal) have been studied and developed into media for reproducing digital information into visual information because such liquid crystal displays have advantages of consuming little electric power and of being fabricated at low cost. However, it is well known that such liquid crystal displays with a memory effect have a demerit that the driving speed is low.
In order to solve this problem, U.S. Pat. No. 5,748,277 disclosed a method of driving such a liquid crystal display. FIG. 6 shows a driving voltage waveform used in the method disclosed by this prior art.
Referring to FIG. 6, the driving method disclosed by U.S. Pat. No. 5,748,277 is described. The driving method comprises a reset step (1) of resetting liquid crystal to an initial state, a selection step (2) of selecting the final state of the liquid crystal, an evolution step (3) of causing the liquid crystal to evolve to the selected final state and a display step (4) of displaying an image. In this method, the selection step (2) is relatively short, and this method is suited for a high-speed drive.
Generally, continuous application of a DC voltage to liquid crystal causes problems such as degradation of liquid crystal molecules. For this reason, it is preferred that liquid crystal is driven by AC pulses.
The above-mentioned U.S. Pat. No. 5,748,277 disclosed a driving voltage waveform which uses AC pulses. According to this prior art, however, the number of inverting the polarity of a pulse voltage applied to liquid crystal is extremely large, which increases the consumption of electric power.